The present invention relates to polysiloxane block copolymers suitable for use in cosmetic and personal care compositions, their preparation, and to cosmetic and personal care compositions, such as hair styling compositions, containing the polysiloxane block copolymers.
Cosmetic and personal care compositions such as hair styling sprays, mousses, gels and shampoos, frequently contain resins, gums and adhesive polymers to provide a variety of benefits, for example, film-forming ability, thickening, sensory properties and hair shaping and setting.
Polymers for use in such compositions include organic or silicone-containing linear or graft copolymers which contain various monomers in an alternating, random, block or homopolymer configuration.
Graft copolymers are known for use as film-forming polymers in hair care and other personal care compositions. These graft copolymers typically comprise a polymeric backbone and one or more macromonomers grafted to the backbone, in which the physical and chemical attributes such as glass transition temperature and water solubility can be selected independently for the polymeric backbone and macromonomer grafts in order to provide the desired overall polymer properties.
For example, WO95/01383 and WO95/01384 describe the use of water or alcohol soluble or dispersible graft copolymers in hair and skin care compositions, in which the copolymer has a backbone and two or more polymeric side chains, and is formed by copolymerisation of randomly repeating monomer units A and B. Monomer A is selected to have a hydrophobic character and macromonomer B comprises a long hydrophilic part. EP 412,704, EP 408,313 and EP 412,707 have suggested the use of silicone grafted acrylate copolymers in hair care applications. U.S. Pat. No. 4,988,506 describes the use of non-pressure sensitive polysiloxane-grafted copolymers in hair care compositions.
Block copolymers have an advantage over graft copolymers in that the polymer architecture can be controlled more closely. This is particularly important when designing polymers with segments of distinct physical and chemical properties for particular applications, e.g. alternating xe2x80x9chardxe2x80x9d and xe2x80x9csoftxe2x80x9d segments in a hairspray polymer for improved hold and feel.
U.S. Pat. No. 5,468,477 describes cosmetics and personal care compositions containing a vinyl-silicone graft or block copolymer comprising a silicone polymer segment and a vinyl polymer segment. This block or graft copolymer is prepared by the free radical polymerisation of a mercapto functional silicone chain transfer agent and vinyl monomers. Copolymers prepared by this method generally have a low molecular weight and a low silicone content due to premature chain termination. Also, intramolecular cross-linking reactions lead to polymer build up in an uncontrolled manner, and hence polydisperse systems with a mixture of chain lengths and molecular architectures. Furthermore, the presence of mercapto groups is a disadvantage in personal care applications since they tend to decompose to give odour problems.
Another approach to the synthesis of block copolymers is to use organopolysiloxane macroinitiators, which are organopolysiloxanes which contain groups which form radicals. These are described in U.S. Pat. No. 5,523,365 and used in WO98/48771, where a polydimethylsiloxane macroinitiator with azo groups is used to synthesise a block copolymer. Problems include the expense and safety hazards associated with the radical macroinitiator, which has to present in significant quantities, otherwise there will be insufficient siloxane content in the final product. Furthermore, the size of the polydimethylsiloxane macroinitiator means that the reaction is inefficient, and large quantities of unreacted silicone have to be removed in a time-consuming extraction process that would be extremely difficult to scale up.
A need exists for conveniently prepared and cost-effective polysiloxane block copolymers for use in cosmetics and personal care compositions.
The present invention provides an improved process for making polysiloxane block copolymers in which end-functionalised polymers are prepared using atom transfer radical polymerisation and then reacted with organopolysiloxanes using a simple nucleophilic displacement reaction, to prepare polysiloxane block copolymers of controlled architecture. Atom transfer radical polymerisation is described in general in Polymer Vol 39, No.21, pp 5163-5170 (Nakagawa et al) and used in WO98/51261 to make graft copolymers.
In a first aspect, the present invention provides a process for making a polysiloxane block copolymer which is built up from units of the formula [A] [B], in which A is a polymeric block built up from radically polymerisable monomer, and B is a polysiloxane block, the process comprising the steps of polymerising a radically polymerisable monomer in the presence of an atom transfer radical initiator to form an polymer which is end-functionalised with a leaving group capable of nucleophilic substitution by nucleophilic end-groups on a polysiloxane, and reacting the polymer with a polysiloxane having nucleophilic end-groups so that a polysiloxane block copolymer is formed via a nucleophilic displacement reaction between the end-groups on the polysiloxane and leaving groups on the polymer respectively.
In a second aspect, the invention provides a polysiloxane block copolymer which is obtainable by the process described above.
The invention also provides a cosmetic and personal care composition, such as a hair styling composition, comprising the polysiloxane block copolymer as described above.